Method for Producing Steel Sheet for Gasket, and Gasket

ABSTRACT

The present invention aims at providing: a method for manufacturing such a kind of gasket-oriented steel plate excellent in elasticity and formability, in a manner to allow for reduction of a breaking elongation of the steel plate to thereby improve a formability (punchability) thereof while improving a proof stress of the steel plate against a repeated stress from a discharge valve to thereby maintain a higher elasticity of the steel plate; and a gasket able to withstand the repeated stress from the discharge valve. The manufacturing method of a gasket-oriented steel plate of the present invention comprises the steps of: annealing a starting steel material having a composition of: Mn less than 0.5%, Ni less than 2.0%, and Cr less than 12.0%; and subsequently temper rolling the annealed starting steel material at a rolling reduction ratio of 10% or more; and the gasket of the present invention is formed by adopting a gasket-oriented steel plate obtained by the above manufacturing method.

TECHNICAL FIELD

The present invention relates to a manufacturing method of agasket-oriented steel plate and a gasket formed by adopting thegasket-oriented steel plate obtained by the manufacturing method of agasket-oriented steel plate, which may be used in a compressor of anautomobile air conditioner or the like, and particularly to amanufacturing method capable of manufacturing a gasket-oriented steelplate excellent in elasticity and formability, and a gasket able towithstand a repeated stress from a discharge valve.

BACKGROUND ART

Conventionally, as a sealing part for oil, gas, and the like to be usedat high temperatures in a field of automobile, a rubber coated metalhaving a structure shown in FIG. 1 is known. In FIG. 1, referencenumeral 1 designates a steel plate, 2 an adhesive layer, 3 a rubberlayer, and 4 a surface coating material layer.

The rubber coated metal shown in FIG. 1 is formed into a gasket as shownin FIG. 2, which is to be widely used in a compressor of an automobileair conditioner. In FIG. 2, reference numeral 5 designates a bead, and 6a retainer.

Examples of functions of a gasket include a shape keeping function as abasic one, and a fluid sealing function by an embossed bead of thegasket.

Further, the functions of the gasket include a particularly importantone to be achieved by a “retainer” drawn at a central part of thegasket. Automobile air conditioners are each configured to use flon as acooling medium, and to conduct an exchange of thermal energy by a cycleof compression, liquefaction, and evaporation of flon. The compressedflon is transferred to a next stage by opening and closing of adischarge valve. The discharge valve is controlled in an opening/closingamount thereof by the retainer fabricated on the gasket. Since thedischarge valve is contacted with the gasket at a frequency on the orderof 4,000 to 9,000 times/minute, the retainer is required to possess ahigher strength and a higher elasticity.

Conventionally, SPCC materials excellent in formability have been used,because more inexpensive dies (such as SKD11 (JIS G4404)) are to be usedin a punching step for a lower cost, for example. However, materialsequivalent to those prescribed in JIS G3141, which are versatilelyavailable from steel plate manufacturers, for example, are excellent informability and insufficient in elasticity, so that such a phenomenon isrecognized that the formed gasket fails to fully withstand a stress froma discharge valve, thereby causing damages of a retainer of the gasket.

Further, although it is possible to provide a countermeasure to cracksof a retainer when a metal having a higher elasticity such as a hightensile strength steel plate is adopted therefor, it is then required touse a punching die having a higher hardness (such as high speed steel,cemented carbide, or the like), which is disadvantageous in cost.

Disclosed in Patent Document 1 is a manufacturing method of a stainlesssteel plate for a flapper valve, and particularly a method formanufacturing a stainless steel plate for a flapper valve, which steelplate has an improved fatigue property, is high in hardness and is thusless in occurrence of burrs after punching, and is subjected to a coldrolling at a rolling reduction ratio of 5% or more. Apparently, it isclassified into a stainless steel plate, because it contains 2.0 to 6.0mass % of Ni, and 12.0 to 20.0 mass % of Cr.

However, no disclosures are found in the technique of Patent Document 1about a cold rolled steel plate (SPCC), because the technique relates toa stainless steel plate.

Meanwhile, described in Patent Document 2 is a manufacturing method of acold rolled steel plate for a gasket material, comprising the steps of:hot rolling a continuously cast article produced by a continuous castingmethod comprising Mn: 0.5 to 3.0%, Ni:≦1.2%, and balance Fe andinevitable impurities; hot rolling it; acid pickling it; and, coldrolling it at a rolling reduction ratio of 30 to 90%. In the PatentDocument 2, it is clarified in its paragraph [0032] that Mn is acomponent required to be included at 0.5% or more so as to prevent redshortness of a primitive plate due to S as an impurity, and to providethe plate with a higher refining degree.

However, when Mn possessing a reinforcing property is added into steelin an amount of 0.5% or more, the steel is considerably increased instrength, thereby bringing about such a problem of formability(punchability) that a specific die made of high speed steel, cementedcarbide, or the like as a press material is required upon punching of aproduct.

-   Patent Document 1: JP2003-41350A-   Patent Document 2: JP2005-36266A

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

It is therefore an object of the present invention to provide: a methodcapable of manufacturing such a kind of gasket-oriented steel plateexcellent in elasticity and formability, in a manner to allow forreduction of a breaking elongation of the steel plate to thereby improvea formability (punchability) thereof while improving a proof stress ofthe steel plate against a repeated stress from a discharge valve tothereby maintain a higher elasticity of the steel plate; and a gasketwithstandable to the repeated stress from the discharge valve.

The other objects of the present invention will become apparent from thefollowing description.

Means for Solving Problem

The above object is carried out by the following inventions.

The invention recited in claim 1 resides in a manufacturing method of agasket-oriented steel plate, comprising the steps of:

annealing a starting steel material having a composition of: Mn lessthan 0.5%, Ni less than 2.0%, and Cr less than 12.0%; and

subsequently temper rolling the annealed starting steel material at arolling reduction ratio of 10% or more.

The invention recited in claim 2 resides in the manufacturing method ofa gasket-oriented steel plate according to claim 1, further comprisingthe steps in the order of:

passing the starting steel material through a hot rolling step, an acidpickling step, and a cold rolling step, before the annealing step.

The invention recited in claim 3 resides in the manufacturing method ofa gasket-oriented steel plate according to claim 1 or 2, wherein thestarting steel material contains Mn in an amount of 0.3% or less.

The invention recited in claim 4 resides in a gasket formed by adoptinga gasket-oriented steel plate obtained by the manufacturing method of agasket-oriented steel plate according to any one of claims 1 to 3.

Effect of the Invention

According to the present invention, it becomes possible: to manufacturesuch a kind of gasket-oriented steel plate excellent in elasticity andformability, in a manner to allow for reduction of a breaking elongationof the steel plate to thereby improve a formability (punchability)thereof while improving a proof stress of the steel plate against arepeated stress from a discharge valve to thereby maintain a higherelasticity of the steel plate; and to provide a gasket withstandable tothe repeated stress from the discharge valve.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of an example of a rubber coated metal;and

FIG. 2 is a plan view of an example of a gasket in a compressor of anautomobile air conditioner.

EXPLANATIONS OF LETTERS OR NUMERALS

-   -   1: steel plate    -   2: adhesive layer    -   3: rubber layer    -   4: surface coating material layer    -   5: bead    -   6: retainer

BEST MODE(S) FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described hereinafter.

In the present invention, the starting steel material upon manufacturinga gasket-oriented steel plate is provided by preparing a general-purposeproduct such as SPCC, SPCD, SPCE, SPCF, and SPCG prescribed by JIS G3141(cold rolled steel plate and steel band) in a manner to contain Mn as achemical component in an amount less than 0.5%. Further, the startingsteel material is configured to contain carbon as an additionalcomponent in an amount of 0.15% or less. Other additional componentscontained in the starting steel material are P, S, and the like, and Feas a remaining component.

The starting steel material in the present invention contains, in itschemical composition, Ni in an amount less than 2.0%, preferably lessthan 1.5%, and Cr in an amount less than 12.0%, and preferably less than10%. Thus, Ni and Cr, if any, are contained in such smaller amounts asnoted just above, respectively, so that the starting steel material ofthe present invention is never matured into such a stainless steel plateas described in JP2005-36266A (Patent Document 2).

In the present invention, Mn is contained in the starting steel materialin an amount less than 0.5%, thereby exhibiting the following effects.Namely, addition of manganese exhibiting a reinforcing property in anamount of 0.5% or more has considerably increased a strength of a steel,thereby bringing about such a problem of punchability that a specificdie made of high speed steel, cemented carbide, or the like as a pressmaterial is required upon punching a product. However, addition ofmanganese in an amount less than 0.5% brings about such an advantagethat a die made of SKD11, which is a general-purpose material, can formthe steel plate.

The method of the present invention for manufacturing a gasket-orientedsteel plate is characterized in that the method comprises the steps of:annealing the above described starting steel material; and subsequentlyconducting a temper rolling treatment at a rolling reduction ratio of10% or more.

Further, although the present invention is not limited in terms of astep(s) before the annealing, it is possible for the starting steelmaterial to be successively passed through the steps in the order of ahot rolling step, an acid pickling step, and a cold rolling step, forexample.

The molten steel having been prepared to have the above chemicalcomponents is smelted by a typically known smelting method using aconverter or the like, and then prepared by a typically used castingmethod such as a continuous casting method into a material to be rolledthen.

Next, the material to be rolled is heated to about 1,200° C., and thensuccessively stretched by rolls while the material is still in a hotstate, in a manner to hot roll the material into a thickness on theorder of 2 to 4 mm at about 600° C. The hot rolling may be adjusted interms of a temperature for processing, a rate for cooling, and the like,thereby allowing for obtainment of various steel materials.

The thermally stretched plate having been hot rolled into a thickness of2 to 4 mm is to be preferably acid pickled. The method for acid picklingis not particularly limited, and examples of usable acids includevarious organic acids or inorganic acids.

After acid pickling, the plate is cold rolled at an ordinary temperatureinto a thickness on the order of 0.1 mm to several mm. “Cold” means thata heat is not particularly applied. It is possible here to conductannealing after cold rolling.

In the present invention, temper rolling is conducted after annealing.It is important in the present invention to set the rolling reductionratio at 10% or more.

The rolling reduction ratio is also called a “temper rolling reductionratio” hereinafter.

Even if all requirements are the same as the present invention, when thetemper rolling reduction ratio is less than 10%, it will lead toinsufficient strain hardening, thereby failing to obtain an appropriateproof stress (of 290 MPa or more, preferably 315 MPa or more) andfailing to withstand a stress from a discharge valve, and therebycausing a damage of a steel plate.

Contrary, as in the present invention, when the temper rolling reductionratio is made to be 10% or more, the temper rolled steel plate issubjected to occurrence of a strain hardening phenomenon where the steelplate is enabled to withstand a repeated stress from a discharge valve,thereby enabling to manufacture such a kind of gasket-oriented steelplate excellent in elasticity and formability, in a manner that thestrain hardening phenomenon allows to decrease a breaking elongation ofthe plate down to less than 33% (preferably down to 30% or less) tothereby improve the formability (punchability) thereof while improving aproof stress thereof to maintain a higher elasticity. Namely, it is thenpossible to obtain an SPCC plate having a breaking elongation decreaseddown to less than 33% (preferably down to 30% or less) to therebyexemplarily decrease burrs, which plate can be in turn formed by aninexpensive die.

The gasket of the present invention is obtainable by exemplarily formingand fabricating the above manufactured gasket-oriented steel plate intoa rubber coated metal. Examples of its shape include one shown in FIG.2.

The obtained gasket exhibits an effect to withstand a repeated stressfrom a discharge valve, by virtue of the properties of the steel plateas a starting material of the gasket.

EXAMPLES

The effects of the present invention will be exemplified hereinafterbased on Examples.

Example 1 to Example 3, and Comparative Example 1 to Comparative Example4

Steel plates listed in Table 1 were formed into rubber coated metals,respectively, and the following evaluations were conducted.

Component analysis values of reinforcing components were obtained asanalysis values of molten steels, respectively.

<Evaluation>

(Mechanical Properties)

No. 5 test pieces specified in JIS Z 2201 were used, and were eachsubjected to measurement of a proof stress (MPa), a tensile strength(MPa), and a breaking elongation (%) all in conformity to JIS Z 2241 bythe following measurement, while adopting a rolling direction of eachsteel plate as a test direction.

(Punchability)

Die: SKD11 was used. In case of failure of punching by means of SKD11, ahigh speed steel was used.

Amount of burr: An amount of burr was measured by a shape measuringinstrument after punching, setting the clearance of 0.06 mm between thepunch and the die.

Cross-section state: A sheared section or broken section after punchingwas visually observed, to evaluate whether it was homogeneous orinhomogeneous.

(Durability to Repeated Stress)

Each rubber coated metal was formed into a gasket, and evaluated forpresence/absence of retainer-crack due to a repeated load from adischarge valve.

<Evaluation Result>

The evaluation result is shown in Table 1.

TABLE 1 Ex. 1 Ex. 2 Ex. 3 Com. Ex. 1 Com. Ex. 2 Com. Ex. 3 Com. Ex. 4Thickness (mm) 0.6 0.6 0.6 0.6 0.6 0.6 0.6 Reinforcing Carbon 0.06 0.060.06 0.04 0.14 0.11 0.06 component amount (%) Manganese 0.3 0.3 0.3 0.30.7 1.2 0.3 amount (%) Rolling reduction ratio (%) 10 12 14 2 2 2 5Mechanical Proof 310 340 400 286 326 530 290 property stress (MPa)Tensile 400 400 412 394 462 800 400 strength (MPa) Breaking 30 23 17 3535 17 34 elongation (%) Punchability Die SKD11 SKD11 SKD11 SKD11 SKD11High speed SKD11 steel⁺ Burr amount 60 60 60 100 100 — 60 (μm)Cross-section Homo- Homo- Homo- Inhomo- Inhomo- — Inhomo- state geneousgeneous geneous geneous geneous goneous Durability against Cracks notCracks not Cracks not Occurrence Occurrence Cracks not Occurrencerepeated stress caused caused caused of cracks of cracks caused ofcracks Note Condition of mass- production ⁺Not punchable by means ofSKD11

The steel plates of Examples 1 to 3 were each punchable by means ofSKD11, less in amount of burr, and homogeneous in cross-section state.Further, retainer-cracks were not caused in gaskets manufactured fromExamples 1 to 3. Example 2 is more suitable for mass-production.

Comparative Example 1 (rolling reduction ratio of 2%) exhibited a proofstress and a breaking elongation, out of appropriate ranges,respectively. Comparative Example 2 (rolling reduction ratio of 2%, andmanganese amount of 0.7%) exhibited a proof stress by virtue of theincreased manganese amount, but exhibited a breaking elongationexceeding an appropriate range. Comparative Examples 1 and 2 exhibitedmore amounts of burr than Examples 1 to 3, and cross-section states ofComparative Examples 1 and 2 were inhomogeneous, respectively.Retainer-cracks were found in gaskets formed from Comparative Examples 1and 2.

Comparative Example 3 (rolling reduction ratio of 2%, and manganeseamount of 1.2%) exhibited an excessively increased strength, and was notpunchable by means of SKD11.

Comparative Example 4 (rolling reduction ratio of 5%) exhibited abreaking elongation exceeding an appropriate range, and itscross-section state was inhomogeneous. Further, retainer-cracks werefound in a gasket formed from Comparative Example 4.

1. A manufacturing method of a gasket-oriented steel plate, comprisingthe steps of: annealing a starting steel material having a compositionof: Mn less than 0.5%, Ni less than 2.0%, and Cr less than 12.0%; andsubsequently temper rolling the annealed starting steel material at arolling reduction ratio of 10% or more.
 2. The manufacturing method of agasket-oriented steel plate according to claim 1, further comprising thesteps in the order of: passing the starting steel material through a hotrolling step, an acid pickling step, and a cold rolling step, before theannealing step.
 3. The manufacturing method of a gasket-oriented steelplate according to claim 1, wherein the starting steel material containsMn in an amount of 0.3% or less.
 4. A gasket formed by adopting agasket-oriented steel plate obtained by the manufacturing method of agasket-oriented steel plate according to any one of claim 1.